If you have ever had a pet with a growth or a mass you may have come across the term mast cell tumor.
To help with communication we will first start with medical terminology clarification. In the world of veterinary medicine, there are certain terms that could be used interchangeably. Examples of this include growth, mass, and tumor. Many lay people associate the term growth with something benign. On the other hand, the term tumor tends to be interpreted as a bad cancer.
I have to admit, knowing this, I do choose my words wisely when communicating with owners.
What About Mast Cell Tumors
Mast cell tumors are one of the most common type of skin tumors in dogs, and the second most common skin tumor in cats. They also tend to behave differently in dogs versus cats.
The trouble with mast cell tumors, as I have found over the years, is that they can look like anything. I have had mast cell tumors look like the classic round, raised, pink, skin growth. I have also had them look like benign skin tags or even feel like subcutaneous, soft, fatty-like growths. This is a reminder that you cannot make a diagnosis based on the appearance of a growth. The only way to confirm what a growth is is with testing.
One key behavior that is specific to mast cell tumors is the ability to grow and shrink from day to day. Mast cells play an important role in the body’s immune system, especially in response to allergic reactions. These are the cells that release histamine, among other mediators, as one of the immune system’s defense mechanisms. These mediators are kept in the granules released by mast cells making them fairly easy to recognize on cytology.
Options For Testing
One option, and easy method for testing, is fine needle aspiration and cytology. This involves taking a needle and syringe to collect cells from the mass. This sample is then placed on a slide, stained, and evaluated under the microscope. This type of testing can give us the information we need in order to determine next steps; however, cytology cannot always give us a definitive diagnosis.
Mast cells. Sample taken from a patient with a mast cell tumor located under the skin on the right caudal hip area (think right butt cheek).
A definitive diagnosis for the majority of masses relies on a biopsy. This involves taking a piece of the tissue for evaluation by a pathologist at the lab. With larger masses this may the preferred option. For smaller masses we usually will remove the entire thing and submit this for histopathology. This testing confirms what the mass is and can also give us information on how aggressive the tumor is. This is especially true for mast cell tumors. There are different ‘levels’ of mast cell tumors from low grade to high grade.
The Difference Between Mast Cell Tumor Grading
Some mast cells will be described as low grade while others are high grade. What this means is that some are more aggressive than others.
Low grade mast cell tumors tend to be less aggressive. These will usually be locally invasive but less likely to spread to other areas in the body.
High grade mast cell tumors on the other hand are bad news. These mast cell tumors will spread to other areas including lymph nodes, internal organs, and potentially lungs.
The prognosis between the two is significant. Patients with low grade mast cell tumors can live out their full life span, usually with no complication. Patients with high grade mast cell tumors require more aggressive surgical removal and additional cancer treatments to extend their life span.
The prognosis is better with low grade mast cell tumors.
Surgery For Mast Cell Tumors
Surgery for most masses should be performed with large margins. This means that the surgical area will include the mass in question with an additional 2cm of surrounding tissue and at least an extra deep layer. Surgical margins are important in order to encompass and remove all cancerous cells. This can prevent regrowth. In the case of high grade tumors the goal is to prevent continued spread throughout the body. In areas that are limited, patients may require radiation therapy or chemotherapy as additional treatments.
For low grade mast cell tumors complete removal is usually curative. Unfortunately this is not the case for high grade mast cell tumors, especially if there has already been spread to the regional lymph nodes. In the case of a high grade mast cell tumor it is recommended to also submit samples from these lymph nodes to evaluate for spread.
Testing is key for any mass and can give us information to prevent further complications with spreading. When in doubt always test especially if there have been changes noted with the masses you have noted on your pet.